Thermal-electric means of airfoil ice prevention



Aug. 17, 1954 C. B. NEEL, JR, ET AL THERMAL-ELECTRIC MEANS OF AIRFOILICE PREVENTION Filed April 13, 1951 FIG. 2

gwum'viiow OAR/i BAKER NEEL,JR

NORMAN R. BERGRUN Patented Aug. 17, 1954 meats THERMAL-ELECTRIC MEANS OFAIRFOIL ICE PREVENTION Carr B. Neel, J r., and Norman R. Bergrun,

Palo Alto, Calif.

Application April 13, 1951, Serial No. 220,960

2 Claims. (Cl. 244-134) (Granted under Title 35, U. S. Code (1952),

see. 266) This invention relates generally to aircraft deicers andspecifically to a de-icer having intermittent action and balancedthermal distribution.

De-icers commonly in use are known to be inefiicient for havingexcessive loads on the aircraft electrical systems and for havingexcessive heat losses in certain areas from which ice i to be removedwhile other areas do not effectively remove ice or prevent itsformation.

An object of the present invention is to provide a de-icer whichoperates intermittently in sections of the area of ice removal, andwhich utilizes the output of the aircrafts generator Without overload.

A still further object of the invention is to provide a de-icer in whichthe heat radiating areas are substantially continuous over the surfaceto be de-iced and in which the shape of th wing is not aerodynamicallychanged.

The exact nature of this invention as wellas other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the annexed drawing in which:

Fig. 1 is an isometric view of a portion of an airplane showing therelative position of the invention.

Fig. 2 is a View in section of the wing taken on line 22 of Fig. 1.

Fig. 3 is a view partly in section showing the positioning of theheating elements relative to the leading edge of the wing.

Fig. 4 is a view partly in section of another inbodiment of theinvention.

Fig. 5 is a schematic view of the electrical circuits of the invention.

Referring now to the drawing in which like numerals indicate like partsthroughout the several views, in Fig. 1, an airplane it is shown hav--ing wings l i, motors I2, wing leading edge It, and ailerons i i. InFigs. 2 and 3, wing H is shown in profile section with an insulatinglayer bonded to the wing surface it by cement or other conventionalmeans. Resistance elements in this particular embodiment are shown asstrips 5'! composed of a metal having resistance to the passage ofelectrical energy and are shown as secured substantially parallel bycement or other means to the insulating layer [5. Strips ii are laidflat and approximately of an inch apart.

In the embodiment shown in Fig. 41, the strips IT are tapered slightlyfrom one end to the other and fixed to the insulating layer I5 withtheir widest ends toward the wing root. This permits the strips tomaintain the distance apart from each other over the span of the wingand over the leading edge of the wing when the wing is tapered ordiminishes in thickness from the root to the tip. It is to beunderstood, of course, that the taper of strips I1 is to besubstantially the same as the taper of the wing span and thickness.

Guter covering it, preferably an electrical insulating varnish, fillsthe interstices between the strips H, l? and forms a protective coatingover the strips to minimize the abrasion effects of ice formingparticles, tapering at it to conform to the wing surface it withoutincrementing to any substantial degree the resistance to airflow overthe Wing.

Tests have shown that the maximum concentration of impinging dropsoccurs slightly below the stagnation point of the airfoil. For asymmetrical airfoil operating vvithout lift this point is exactly at theleading edge of the wing. For airfoils operating with lift thestagnation point usually occurs below the leading edge. Therefore, thisinvention contemplates that for meteorological conditions usuallyencountered in flight, the heating intensity should be of the order of 8watts per square inch for an airfoil section of 8 ft. chord length andflight speed of about 200 M. P. H. In order that unduly high surfacetemperatures on the balance of the heated surface do not overheat thesurface and cause a possible breakdown of the insulating layer, a heatintensity of 5 or 6 watts per square inch is adequate for most icingconditions.

It has been found that the accretion of ice is greatest at points Aonthe leading edge of the wing (Fig. 2), the so-called stagnation point,and that areas 28 and C, respectively, 10 and 15 per cent of the chordlength D are subject to ice accretion to a degree which impairs theaerodynamic qualities of the wing. Therefore, while it is not to beconstrued that this invention is limited in application to just thoseareas in any fixed proportion, nor used solely upon wing surfaces, ithas been found that the most efficient removal of ice is obtained by theuse of the de-icer in the areas named.

In Figs. 3 and 4 it will be seen that strips l? and H are grouped insections 2i), 2!, and 22, for example, and each section is separatedfrom the next by sufficient distance to permit connections to theelectrical system, here shown in exaggerated detail, but generally 1; ofan inch is ade-- quate. The strips ll, ll are connected electrically byleads 23 and 24 to the aircraft electrical system to be described later.At area A, strips H, H are connected together in parallel, as anexample; at areas B and C, they are connected to the leads 23 and 24singly where they are closest to area A, and are connected in serieswhere they are farthest from area A. It will be seen, therefore, thatthe heat radiatingfrom the sections 29, 2 i, 22, is'greatest along thestagnation point of the leading edge and is less at the edges of each.section on th upper and lower surfaces of" the wing.

In Fig. 5, the current leads24, which in Figs. 3.

and 4 are shown entering holes 25 in the wing surface I6, are eachconnected to one of the hot leads 33 that are in turn connected togenerator 26 which supplies current to.the..loads Il ofthe individualsections 2|], 2! and22'. The return leads 23 are each connected to thecommon new 4 tions of icing and to remove the ice accumulationeiiiciently and Without danger. Also, it is entirely likely that thosesections adjacent the airplanes engines and exhaust pipes may not needas frequent de-icing or. as much heat radiation.

The timer-s28, 29, and 30 may be adjusted to operate spanwise, insequence, and in unison with i a corresponding section on the other wingin order that the wings of the airplane have identical liftingcharacteristics at all times.

Obviously many modifications and variations of thepresent invention arepossible in the light of, the above teachings. It is therefore to be un-7 derstood, that within the scope of the appended tral lead 34 tocomplete the circuit between the generator and the loads. from firescaused by short-circuiting of the deicing system afuse 35 and a circuitbreaker 3! are positioned in each of thehot leads 33 ahead of the leads24, and'a circuit'breaker relay 2l'is To protect" the aircraft 1connected between the'neutrallead 34 and ground at a point between thereturn leads 23. and the generator. Therelay- 2! is-of a commoncommercial typ and isoperatively connected to the circuit breakers 3!tomaintain them in a closed position during the normal operatingsequence of the de-icer system. Whenever the system is shorted out, therelayis energized to open the circuit breakers, thus interrupting thehow of ourrent to the loads l'i'. Any inadvertent grounding of any ofthe de--icer groups will'energize the relay '2'! Which will in turn openthe circuit via'circuit breaker 3 I.

Timers 28,29, and-3B, are BZLOhICOIlIlGClJEd in one of the returnleads-2 3= and are interconnected with manual control 32 'for adjustmentof the intervals of operation. It is to be understood, of course, thatwhile only'three sections 20, 2 i, and 2-2 are shown, and a like numberof timers 23, 29, and 3li,the number-of sections and associated timersmay be varied to provide heating to areas Wherever desired on theaircraft;

In operation, it has been proved'by experiments that certain areas ofthe wing surface require dee icing oftener than others; thatzit" isdangerous to allow ice to accumulateon those surfaces which havefollowing tail surfacesor control devices,

While at'the wingtips, for-instancathe removal of a greater quantity ofice. at one time does not present any particular. hazard; It will beseen, therefore, that the particular'a'rrangement ofthe timer sequencescan be variedto meet all condiclaims, the invention may be practicedotherwise 'than'as' specifically described.

The invention described herein may be manufactured and used by or forthe Government of the U ited States of America for governmental purposesWitl'iout the payment of any royalties thereon or therefor.

What claimed is:

1'. In an airfoil having a leading edge-with'a stagnation area'ofhighrate of ice accretion relative to the remainderof-the airfoil, a deicer. 5y"- tem comprising a source. or" electrical power, a plurality ofcircuit breakers" connected to said source, a circuit breakeri'elay'grounded to the airfoil and connected to said source, a conductorconnected to each circuit breaker, resistance strips connected to theleading edge of said air foil and tosaid conductors, the strips atstagnation area. being connectedin parallel id the'adjacent strips beingconnected in serie and also singly, and timers 1 to control the durationoi operativeness of said strips connected to said conductors betweensaid relay and said resistance strips,

2. The system of claim land; said airfoil having spaced apertures in itthrough which said conductors are passed.

References Cited; in the-file of: this patent UNITED STATES PATENTS

